We propose to purchase a Perkin-Elmer, ELAN 250 Inductively Coupled Plasma/Mass Spectrometer (ICP/MS) for collaborative research in human nutrition. The instrument will be housed in the Trace Element/Mineral Core Laboratory of the University of Chicago Clinical Nutrition Research Unit. The instrument will be used for stable isotope analysis in tracer studies in humans. Five major uses are identified, including: Dr. V. Young, "Zinc and Copper Metabolism in the Elderly"; Dr. S. Burstein, "Zinc Absorption and Status in Children with Sickle Cell Disease"; Dr. D. Schoeller, "Measurement of Extracellular Water with Bromine"; Dr. S. Fomon, "Iron Retention in Infancy"; and Dr. M. Janghorbani, "Assessment of Selenium Status in Man". We have also identified three minor users who are interested in development of magnesium tracer methods for mineral metabolism studies and the measurement of zinc status in adults. These studies depend on the ability to measure stable isotopes of these trace elements and minerals. Instrumentation for these studies is not currently available at the University of Chicago.